<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>3-1</title>
    <style type="text/css">
        pre{color:green;padding:10px 15px;background:#f0f0f0;border:1px dotted #333;font:12px/1.5 Coursier New;}
        span{color:#999;}
    </style>
</head>
<body>
<pre>
 <script type="text/javascript">
  alert(typeof 12345);
  alert(typeof "abc");
  alert(typeof document);
 </script>
</pre>
<script type="text/javascript">
    alert("typeof 12345 ->" + typeof 12345 + "\
       \n\n typeof \"abc\"->"+ typeof "abc" + "\
       \n\n typeof document ->"+ typeof document);
</script>
</body>
</html>